Exhaust Issue?

[MikeB]

Mike, check "fig. A" shown in your merc manual, spacer with the vent hole. The notes say that spacer is for engines mounted level, such as yours.

John, I see that now that you mention it.  I believe the block-off plate that I have does include a vent hole:

[Glastronjohn18]

Just to be sure I went out and checked to see what was on my engine( '80 CVX 18). Sure enough it has the vent hole. The other ports are blocked off, as in your spacer.
That should end the confusion.




Here is the spacer with the gasket.

[MikeB]

Wow, thanks for doing that John!  Sounds like I'll be picking up another plate for the port side. 

New theory:  If water is flowing too easily on the port side (no block-off plate), wouldn't that put less water passing through the starboard side? 

[Glastronjohn18]

Here is my theory. Unrestricted water supply flows thru riser too fast for heat to radiate into it(the water) causing the riser to stay hot.Perhaps there is a blockage elsewhere in the riser.

[Retro Performance]

Mike ..................I see we had a cancellation in service for Monday 7-8-13..........if you would like to fill that slot let me know.  I can check a couple things in Mercnet, what is your serial number?


Retro

[Glastronjohn18]

Sierra-Marine seems to think I need to same block-off plate (without holes) that I'm using now: 

Don't forget NAPA handles Sierra parts.

[MikeB]

Mike ..................I see we had a cancellation in service for Monday 7-8-13..........if you would like to fill that slot let me know.  I can check a couple things in Mercnet, what is your serial number?


Retro

Retro - thanks for the offer!  I was in there earlier today to buy a block-off plate.  If that doesn't work I'll see you on Monday.  

Serial number is 5528624

[OleRed]

I been trying to figure how the water gets from the logs thru the riser with only the vent hole in the seperator plate, there is a by-pass port in the thermostat housing for constant flow to the risers, before the thermostat opens, but when the thermostat does open, all the water goes thru the riser hose also.

[Retro Performance]

If the hose is removed from the overheating riser while the engine is running is there good water flow?  Clear hoses can be installed to moniter.....I would think both sides should flow the same?

[Rich_V174SS]

The way I'm reading it is your logs are part of the engine water circulation and once full the extra water bypasses through the T-stat housing and out through the elbows. When the T-stat opens additional water from the engine mixes with the bypass water and new water enters the block. The T-stat only has to open a little to regulate the engine temperature. So, I think a lot of your problem is from the fact you don't have a block-off plate in the other side and all of your engine's circulated water is going up and out of the engine with none going through the bypass to cool the side that's getting hot. When you get two block-off plates installed the system will be balanced.

[Rosscoe]

Mine are GLM's but this is what the gaskets look like. They may flow differently then stock Mercrusiers though.

[MikeB]

Finally broke down and bought one of these so I can be more accurate with my temperatures:



Opened up the starboard elbow this morning and installed my new block-off plate.  A few things I noticed:

- Temperatures immediately felt better.  If anything, the port side is now getting a little warmer than the starboard side.  
- at idle, both manifolds sat right around 150f.  Port elbow about 140f and starboard elbow 115f.  
- put it into low gear and both elbow temps drop to 110f.  Both manifolds stay around 150f.  Both exhaust bellows are roughly same temp as elbows.  There must be significantly more water flow when low speed trolling.  
- temperature gauge on dash now reads 140-150f, which sounds more accurate.  Before it would only read around 120f.  

After a few careful tests trolling we decided to go skiing for 20 minutes or so.

- Went around 30mph for 20 minutes.  
- Manifold temps on both sides around 170f.  
- elbow temps about 130f.  
- temp gauge on dash about 150f.  
- No more "burn your skin off" exhaust bellows!

I like these readings much more, and especially thrilled that both sides seem more consistent with each other.

One thing I did notice when I had the thermostat housing apart -  the PO stuck a 160f thermostat in.  Looks like the service manual suggests 143f for my engine.  Is that something I need to switch?

[Jason]

If you are running 150 on the temp gauge I would not change out the thermostat. Sounds like it's all dialed in now! Nice work.